This part of the Program Project deals with the sarcoplasmic reticulum and surface membrane of cardiac muscle. Its overall aim is to determine how these two membrane systems regulate the myoplasmic Ca2+ concentration in cardiac muscle and how this regulatory process is altered in ischemic muscle cells. In isolated sarcoplasmic reticulum membrane preparations, a "Ca2+ release channel" mediates Ca2+ fluxes with physiological rates suggesting a role in excitation-contraction coupling in muscle. Regulation of this channel by Ca2+, Mg2+, adenine nucleotides, calmodulin, and other factors will be determined, using radioisotope flux - rapid quench techniques. In addition, Ca2+ release channels of cardiac sarcoplasmic reticulum will be incorporated into planar lipid bilayers so that single channel conductance, ion selectively and voltage-dependence, as well as the kinetics of channel opening and closing can be investigated. The effect of drugs will be tested to suggest ways of identifying and purifying the Ca2+ release channel components as well as modifying Ca2+ release in vivo. The Ca2+ permeability and Ca2+ transport properties of the surface membrane will be analyzed with membrane fractions isolated from ischemic and nonischemic hearts.